Method of curing condensed siloxane resins



United States Patent 065cc 3,015,646 Patented Jan. 2, 1962 METHOD OF CURING CONDENSED SILOXANE RESINS John L. Speier, Midland, Mich assignor to Dow Corning Corporation, Midland, Mich, a corporation of Michigan No Drawing. Original application Feb. 14, 1955, Ser.

No. 488,163. Divided and this application Aug. 28,

1958, Ser. No. 757,699

6 Claims. ((31. 260-465) This application relates to a method of curing completely condensed organosiloxane resins.

This application is a division of copending application Serial No. 488,163, filed February 14, 1955 (now US. Patent No. 2,925,402). The latter is a continuation-inpart of applicants copending application Serial No. 463,061, filed October 18, 1954 (which was itself a continuation-in-part of Serial No. 398,896, filed December 17, 1953 and both of which are now abandoned), and of copending application Serial No. 463,062, filed October 18, 1954 (which is now US. Patent No. 2,723,987, issued November 15, 1955, and which was a continuatoin-inpart of Serial No. 398,897, filed December 17, 1953, now abandoned).

It has long been known that organosiloxane resins make excellent high temperature coatings for metal and other surfaces. it has also been known that these coatings tend to be more corrosion resistant than do similar coatings made from organic materials. However, the organosiloxane coatings heretofore employed, especially those which contain only organosilicon resins, require higher temperatures and longer curing time than is needed for most organic finishes. In general, organosilicon resins heretofore commercially available protect metal and glass surfaces from corrosion better in most cases than organic' resins. However, these previously employed organosilicon resins leave much to be desired in the way of protection for metal surfaces under rigid conditions such as those encountered in sea water and the like.

It was known prior to this application that completely condensed organosiloxanes, i.e., siloxanes containing no silicon bonding hydroxyls, could be employed for coating base members. However, as is shown in US. Patent No. 2,610,169, these materials require even higher temperatures and more prolonged curing schedules than the more commonly employed hydroxylated siloxane resins. The present invention relates to a method of curing siloxane resins which obviates the above difficulties.

It is the object of this invention to provide a method of curing completely condensed organosiloxane resins at suiiiciently low temperatures and in a sufliciently short period of time so that the curing will be commercially feasible. Another object is to provide superior silicone resin coatings for metal and other surfaces. Other objects and advantages will be apparent from the following description.

This invention relates to a method of curing completely condensed copolymeric siloxanes containing from to 75 mol percent siloxane units of the formula in which X is a functional radical of the formula (YOOC),,Rin which R" is a divalent or trivalent saturated aliphatic or cycloaliphatic hydrocarbon radical wherein each carbonyl group is attached to at least the third carbon atom away from the silicon atom, Y is an alkyl radical or hydrogen atom and a is an integer from 1 to 2 inclusive, R is of the group monovalent hydrocarbon radicals free of aliphatic unsaturation and halogenated monovalent hydrocarbon radicals free of aliphatic unsaturation and n has a value from 0 to 2, the remainder of the siloxane being composed of siloxane units of the formula z,..sio

in which Z is of the group monovalent hydrocarbon radicals and halogenated monovalent hydrocarbon radicals and m has an average value from 0 to 3 inclusive and in which copolymeric siloxane the average ratio of total organic groups to silicon ranges from 1 to 1.7, by heating a mixture of said siloxane and a polyfunctional organic curing compound capable of condensing with the X groups in the siloxane to give cross linking, until the siloxane is cured.

In carrying out the method of this invention it is only necessary to mix the silcxane and the polyfunctional organic curing compound in the desired proportions and thereafter heat until a satisfactory cure is obtained. The curing temperatures vary with the reactants employed but may range from 30 C. up to 250 C. or higher. In general, satisfactory cures may be obtained in the temperature range from to C. for periods of 30 minutes or less. The curing operation may be either a one or more step process. Thus the mixture of siloxane and organic curing compound may be partially reacted and the product thereafter molded or appliedas a coating and the curing completed by further heating: Alternatively, the mixture may be heated continuously until a satisfactory cure is obtained.

The method of this invention is particularly adaptable for the application of siloxane protective coatings in which the base member can be dipped in a mixture of the siloxane and the curing compound and thereafter heated until the film is cured.

The proportions of the functional units in the siloxane should be at least 5 mol percent in order to obtain satisfactory cures. The upper limit will be determined by the thermal stability desired in the finished product. It a high degree of thermal stability is desired, the organofunctional siloxane units should be present in amount of 5 to 20%. This reduces the amount of organic material present in the resin and hence the stability of the cured film is essentially the same as that of conventional silicone resins. If thermal stability is not the primary factor in the final product, higher amounts of the organofunctional siloxanes with a proportional increase in the amount of organic curing agent may be employed.

It should be understood that siloxanes containing both silicon bonded OH groups and the X groups above-defined can be cured by beating them with organofunction'al curing agents. However, such a process does notgive cured resins equivalent to those prepared by the method of this invention.

The functional organc-silicon compounds ofthe type XRnSlO with the method set forth in said application.

If desired the siloxanes employed herein can contain one or more than one type of units. R" can be any divalent saturated aliphatic hydrocarbon radical of at least 3 carbon atoms such as propylene, butylene and octadecylene or any trivalent aliphatic saturated hydrocarbon radical of at least 3 carbon atoms such as and or any cyclic divalent aliphatic hydrocarbon radical of at least 5 carbon atoms such as cyclohexylene, cyclopentylene, methylcyclopentylene, and

S S l and any trivalent cycloaliphatic saturated hydrocarbon radical of at least 6 carbon atoms such as a (I I\/W CH2 and CH: S

It should be understood that the term carboxyl group as employed herein includes the group COOH and COOY in which Y is an alkyl radical such as methyl ethyl or octadecyl.

In the organofunctional siloxane units R can be any monovalent hydrocarbon radical free of aliphatic unsaturation such as alkyl radicals such as methyl, ethyl and octadecyl; cycloalkyl radicals such as cyclohexyl and cyclopentyl and aromatic hydrocarbon radicals such as phenyl, benzyl, tolyl, naphthyl and xenyl. R can also be any halogenated monovalent hydrocarbon radical free of aliphatic unsaturation such as chlorophenyl, dibromoxenyl, tetrafluoroethyl, pentafiuorobutyl and a,a,a-trifiuorotolyl.

For the purpose of this invention the organosiloxanes of the formula znsio can be any siloxane in which Z is any monovalent hydrocarbon radical such as alkyl radicals such as methyl, ethyl and octadecyl; alkenyl radicals such as vinyl and allyl; cycloaliphatic radicals such as cyclohexyl, cyclopentyl and cyclohexenyl and aromatic hydrocarbon radicals such as phenyl, benzyl, tolyl, naphthyl and xenyl and any halogenated monovalent hydrocarbon radical such as chlorophenyl, trifluorovinyl, tetrafluorobutyl, tetrabromoxenyl and a,a,a-trifluorotolyl. The siloxanes can be either homopolymers or copolymers and there can be more than one type of Z group attached to any one silicon atom and the units can be ZSiO Z SiO and Z SiO together with limited amounts of SiO;, units.

The relative proportions of the siloxanes and the polyfunctional organic curing compounds are not critical. Obviously, however, the most eificient operation will be obtained when the organic curing agent is employed in amounts approximately equivalent to the functional X groups in the siloxane. Thus the most efiicient operation will usually occur in the range from that in which the organic curing compound is present in amount such that there is one of its functional groups for every COOH and 4 COOY group in the siloxane to that in which there is one mol of organic curing compound per mol of XR,.si0

method of this invention is specifically exemplified in their superior resistance to attack by chemical reagents. This is shown by the fact that metal surfaces which are coated with the resins prepared by the method of this invention show much less corrosion when exposed to salt water, caustic and acid than resins prepared from conventional organosiloxanes. The method of this invention is equally applicable for the preparation of siloxane molding compositions, laminates and cast articles.

The following examples are illustrative only and should not be construed as limiting the invention which is properly delineated in the appended claims.

EXAMPLE 1 97 g. of phenylmethyldichlorosilane, 20.8 g. of methyltrichlorosilane and 29.4 g. of phenyltrichlorosilane, 19 g. of diphenyldichlorosilane and 40 g. of

were dissolved in 250 ml. of toluene and 154ml. of diethylether and hydrolyzed with water. During hydrolysis the mixture was cooled in an ice bath and made almost neutral with sodium hydroxide. The organic layer was washed until neutral, stripped of ether and azeotropically dried. It was then completely condensed by refluxing in a 25% toluene solution for 6 hours with potassium hydroxide in amount of .2% by weight based on the weight of the resin solids. The resulting solution Was free of silicon-bonded hydroxyls and was neutralized, washed and dried. The solution was concentrated to 70% by weight solids. The resulting siloxane was the copolymer having the composition 50.8 mol percent phenylmethylsiloxane, 13.9 mol percent monomethylsiloxane, 13.9 mol percent monophenylsiloxane, 7.5 mol percent diphenylsiloxane and 13.9 mol percent 9.3 g. of the above siloxane, equivalent to .01 mol M00 0 C- jSiCla MeOOC SiO CHj I was mixed with 1.2 g. (.01 mol) of hexamethylene diamine and heated at 250 C. for 2 hours in a nitrogen atmosphere. The resulting viscous resin was dissolved in 5 g. of toluene. In this resin the carboxymethyl group had been converted into an amide having the formula Panels of sheet iron were dip coated with a toluene solution of this resin (A) and were compared with a commercial phenylmethylpolysiloxane resin (B) having the composition 50.8 mol percent phenylmethylsiloxane, 27.8 mol percent monomethylsiloxane, 13.9 mol percent monophenylsiloxane and 7.5 mol percent diphenylsiloxane which contained about 1.5% silicon-bonded OH groups and a small amount of a zinc naphthenate catalyst. The

panels were cured as shown inthe table below and were immersed in a saturated aqueous sodium chloride solution at 90-95 C. and the effect on the film was noted as shown in the table. Plate glass was coated with resins (A) and (B) and the resulting panels cured as shown in the table below and then immersed in concentrated aqueous NaOH and toluene at 30 C. for the times shown.

Table I Immersion Media Resin Curing Schedule Results Air dried in min A {150 0. for 15 min"-.- f figg m Saturated aqueous 250 C. for 15 min fa l. B Identical Film blistered and broke in A d d 4 hrs.

lir rie 15 min A {150 o. for 15 min gi Concentrated 230 C. for 1 hour. ay

aqueous NaOH. Identical Film softened and loosened in 2 days A Identical softened in Toluene 1 B Ident1cal Completely dissolved in 1 min.

EXAMPLE 2 Equivalent results were obtained when 'diethylene triamine is employed in the procedure of Example 1.

EXAMPLE 3 When a completely condensed copolymer of 35 mol percent monophenylsiloxane and 65 mol percent of the siloxane is heated with hexamethylene diarnine in accordance with the procedure of Example 1 a cured siloxane resin is obtained.

EXAMPLE 4 When a completely condensed copolymer of 50 mol percent phenylmethylsiloxane, mol percent a,u,a-trifluorotolylsiloxane and 25 mol percent HO O C SiO1.a

HO O

is mixed with hexamethylene diamine in amount such that there is one amino group per one carboxyl group in the mixture and thereafter heated at 150 C. for minutes, a cured siloxane resin is obtained.

That which is claimed is:

l. A resinous coating composition in which the resinforming constituent consists essentially of a mixture of 1) a completely condensed copolymeric siloxane containing from 5 to 75 mol percent siloxane units of the formula in which X is a functional radical of the formula (YOOC) R"- in which R" is a radical of at least three carbon atoms and is of the group consisting of divalent and trivalent saturated aliphatic hydrocarbon radicals and divalent and trivalent saturated cycloaliphatic hydrocarbon radicals in all of which each carbonyl group is attached at least the third carbon atom 6 away from the silicon atom, Y is of the group consisting of alkyl radicals and hydrogen and a is an integer from 1 to 2 inclusive, R is of the group consisting of monovalent hydrocarbon radicals free of aliphatic unsaturation and halogenated monovalent hydrocarbon radicals free of aliphatic unsaturation, n has an average value from O to 2, the remainder of said siloxane being composed of siloxane units of the formula ZmS1O4' m in which Z is of the group consisting of monovalent hydrocarbon radicals and halogenated monovalent hydrocarbon radicals and in has an average value from O to 3 inclusive, said copolymeric organosiloxane having an average of from 1 to 1.7 inclusive total organic groups per silicon atom and (2) a diamine.

2. A resinous coating composition in which the resinforrning constituent consists essentially of a mixture of (l) a completely condensed copolymeric siloxane containing from 5 to 75 mol percent O Si C O OMe units, the remainder of said siloxane being methyl and phenyl siloxane units, said siloxane having on the average from 1 to 1.7 inclusive total organic groups per silicon atom and (2) an aliphatic diamine.

3. A composition in accordance with claim 2 in which the diarnine is hexamethylene diamine.

4. A resinous coating composition in which the resinforrning constituent consists essentially of a mixture of 1) a completely condensed copolymeric siloxane containing from 5 to 75 mol percent siloxane units of the formula [(YOOC) R"]SiO in which R is a radical of at least 3 carbon atoms and is selected from the group consisting of divalent and trivalent saturated aliphatic hydrocarbon radicals and divalent and trivalent saturated cycloaliphatic hydrocarbon radicals in all of which each carbonyl group is attached to at least the third carbon atom away from the silicon atom, Y is selected from the group consisting of alkyl radicals and hydrogen, and a is an integer from 1 to 2 inclusive, the remainder of the siloxane being composed of siloxane units of the formula in which Z is selected from the group consisting of monovalent hydrocarbon radicals and halogenated monovalent hydrocarbon radicals and in has an average value from O to 3 inclusive, said copolymeric siloxane having an average degree of substitution of from 1 to 1.7 inclusive total organic groups attached to silicon by carbon-silicon linkage per silicon atom, and (2) a diamine.

5. A resinous coating composition in which the resinforming constituent consists essentially of a mixture of 1) a completely condensed copolymeric siloxane containing from 5 to 75 mol percent siloxane units of the formula [(YOOC) R"]SiO in which R" is a radical of at least 3 carbon atoms and is selected from the group consisting of divalent and trivalent saturated aliphatic hydrocarbon radicals and divalent and trivalent saturated cycloaliphatic hydrocarbon radicals in all of which each carbonyl group is attached to at least the third carbon atom away from the silicon atom, Y is an alkyl radical, and a is an integer from 1 to 2 inclusive, the remainder of the siloxane being composed of siloxane units of the formula zmsio in which Z is selected from the group consisting of monovalent hydrocarbon radicals and halogenated monovalent hydrocarbon radicals and m has an average value from to 3 inclusive, said copolymeric siloxane having an average degree of substitution of from 1 to 1.7 inclusive total organic groups attached to silicon by carbon-silicon linkage per silicon atom; and (2) a diamine.

6. A resinous coating composition in which the resinforming constituent consists essentially of a mixture of (1) a completely condensed copolymeric siloxane containing from 5 to 75 mol percent siloxane units of the formula in which X is a functional radical of the formula (YOOC),,R" in which R is a radical of at least three carbon atoms and is of the group consisting of divalent and trivalent saturated aliphatic hydrocarbon radicals and divalent and trivalent saturated cyclol-iphatic hydrocarbon radicals in all of which each carbonyl group is attached at least the third carbon atom away from the silicon atom, Y is of the group consisting of alkyl radicals and hydrogen and a is an integer from 1 to 2 inclusive, R is of the group consisting of monovalent hydrocarbon radicals free of aliphatic unsaturation and halogenated monovalent hydrocarbon radicals free of aliphatic unsaturation, n has an average value from 0 to 1, the remainder of said siloxane being composed of siloxane units of the formula References Cited in the file of this patent UNITED STATES PATENTS 2,570,090 Barry et al. Oct. 2, 1951 2,601,237 Barry et al. June 24, 1952 2,687,418 Sommer Aug. 24, 1954 2,721,856 Sommer Oct. 25, 1955 2,723,987 Speier Nov. 15, 1955 2,819,245 Shorr Jan. 7, 1958 

1. A RESINOUS COATING COMPOSITION IN WHICH THE RESINFORMING CONSTITUENT CONSISTS ESSENTIALLY OF A MIXTURE OF (1) A COMPLETELY CONDENSED COPOLYMERIC SILOXANE CONTAINING FROM 5 TO 75 MOL PERCENT SILOXANE UNITS OF THE FORMULA 